1. Field of the Invention
The invention relates to a hybrid vehicle. More particularly, the invention relates to a hybrid vehicle configured so that an electricity storage device mounted in the vehicle can be charged by an electric power source provided outside the vehicle.
2. Description of Related Art
In recent years, there have been proposed hybrid vehicles in which an on-board electricity storage device is charged with electric power from an electric power source provided outside the vehicle (an external electric power source) such as a commercial electric power source or the like. A vehicle whose electricity storage device is chargeable from an external electric power source is referred to as a plug-in type hybrid vehicle. A plug-in type hybrid vehicle achieves high energy efficiency when it travels while keeping the engine in a stopped state as much as possible. Therefore, one of two travel modes, that is, a travel mode that maintains the stopped state of the engine and uses only an electric motor as a drive force source or a travel mode that uses both the engine and the electric motor, is selectively engaged. The travel mode in which the engine is kept in the stopped state and only the electric motor is used as a drive force source is referred to as the EV (electric vehicle) traveling. The travel mode in which the engine and the electric motor are used is referred to as the HV (hybrid vehicle) traveling.
A plug-in type hybrid vehicle has two electric power source modes of charging the electricity storage device. The two electric power source modes are supply of electric power to the electricity storage device based on electric power generating operation that utilizes motive power of the engine and supply of electric power to the electricity storage device from an external electric power source. Hereinafter, the charging of the electricity storage device during the HV traveling is expressed also as “internal charging”. Furthermore, the charging of the electricity storage device from an external electric power source is expressed also as “external charging”. Japanese Patent Application Publication No. 2010-167898 (JP 2010-167898 A) discloses one form of a control of the charging of the electricity storage device. Specifically, the publication describes a hybrid vehicle that avoids the engine being operated for the purpose of the internal charging if the external charging has started and the SOC (state of charge) of the electricity storage device is smaller than a predetermined lower limit value.
In the plug-in type hybrid vehicles, if at the time of the external charging, the electricity storage device is charged to a fully charged level, the cruising range at the time of EV traveling (hereinafter, also referred to as “EV traveling distance”) can be extended. This improves fuel economy. Furthermore, this also reduces the amounts of emissions. However, in a usage manner where only the internal charging is repeatedly performed, it becomes difficult to appropriately secure opportunities for the external charging. As a result, the EV traveling distance declines. Therefore, there is possibility that the advantages of the plug-in hybrid vehicle cannot be fully exploited.